There is known a two-wheeled motorcycle provided with an air cleaner unit for purifying air and introducing the purified air to an engine (for example, see FIGS. 1 to 3 of Japanese Patent Application Laid-Open Publication No. 2005-105988 (JP '988)).
As shown in FIGS. 1 to 3 of 'JP 988, an air introducing passage (30) is arranged on the outside of a main frame (5) (a number with parenthesis designates a reference number of 'JP 988, those that follow are the same). An air cleaner box (18) (hereinafter, referred to as “air cleaner unit (18)”) is arranged on the inside of the main frame (5). A V-type engine (10) for sucking the air purified by the air cleaner unit (18) is located below the air cleaner unit (18).
Lightening holes (42) are formed in the main frame (5). Left and right air intake ducts (43) extend to the air cleaner unit (18) in such a way as to pass through the lightening holes (42). Air introducing passages (30) are configured to communicate with the air intake ducts (43). The air passes through the air introducing passages (30) and enters the air cleaner unit (18) through the left and right air intake ducts (43). After purified by the air cleaner unit (18), the air flows into the engine (10).
In order to lightening the air cleaner unit as above, it is conceivable to use a relatively light carbon fiber as a material of the air cleaner unit. In the case of the air cleaner unit using the carbon fiber, it may be required to provide a reinforcing rib for reducing or suppressing noises and vibrations. In the case of forming a rib structure by the carbon fiber, the forming of the rib may take a lot of time to thereby cause an increase in cost. As a countermeasure against the above, when a layer of the carbon fiber is thickened, it is possible to reduce or decrease air intake noises and vibrations. However, there is a problem that a capacity of the air cleaner unit is decreased with increase in thickness of the layer of carbon fiber.
It is desired to provide a technique which is capable of reducing or decreasing the air intake noises and vibrations and ensuring the capacity of the air cleaner unit.